Improved relaying in a wireless communication network

ABSTRACT

A first type node (AP 0 , AP 1 , AP 2 ) in a wireless communication system ( 1 ), wherein the first type node (AP 0 , AP 1 , AP 2 ) is adapted to: —communicate with at least one other first type node (AP 0 , AP 1 , AP 2 ) in the wireless communication system ( 1 ) over a corresponding channel (h A01 , h A12 ), and —transmit a first plurality of signals (x 11 , x 1i , X 1N , X 21 , X 2i , X 2N−1 ) to the other first type node (AP 0 , AP 1 , AP 2 ). In the case of the other first type node (AP 0 , AP 1 , AP 2 ) requesting re-transmission of a failed signal (x 11 ) in the first plurality of signals (x 11 , x′ 1i , X 1N , X 21 , X 2i , X 2N−1 ), the first type node (APo, AP 1 , AP 2 ) is further adapted to: —receive a limit of tolerable interference from the other first type node (APo, APi, AP 2 ), and —re-send the failed signal (xn) in a second plurality of signals (x 11 , x′ 2i  x′ 1i , X′ 1N , X′ 21 , X′ 2N−1 , X′ 2N , X 2N ; X 11 , x′ 2i , x′ 1i , X′ 1N , x′ 21 , x′ 2N−1 , X 2N ) to the other first type node (AP 0 , AP 1 , AP 2 ) while sharing the spectrum for the failed signal (x 11 ) with an additional signal (x′ 2i ) without exceeding the limit of tolerable interference.

TECHNICAL FIELD

The present disclosure relates to relaying in wireless communicationnetworks, in particular in integrated access and backhaul (IAB)networks.

BACKGROUND

The fifth generation of wireless networks (5G) must provide high-ratedata streams for everyone everywhere at any time. To meet such demands,it is required to use large bandwidths. Here, it is mainly concentratedon millimeter wave-based, potentially, massive multiple-input andmultiple-output (MMIMO), links as a key enabler to obtain sufficientlylarge bandwidths/data rates. Importantly, the presence of very widebandwidths makes it possible to include the wireless backhaul transportin the same spectrum as the wireless access. In such a setup, there isthus a sharing of radio resources between access and backhaul linkswhich implies that access and backhaul links compete over the same radioresources pool.

For this reason, 3GPP has considered such integrated access and backhaul(IAB) network configurations where an access point (AP), that forexample can be fiber-connected, provides other APs as well as thecustomer-premises equipments (CPEs) inside its cell area with wirelessbackhaul and access connections, respectively. The access-integratedbackhaul link can either be a single-hop or multi-hop link in an IABnetwork. In a multi-hop deployment, the IAB network from one AP isrelayed along a certain route from AP to AP until it reaches itsdestination. IAB networks can thus have either star-like configurationwith multiple APs wirelessly backhauled through direct single-hopconnections to the fiber-connected AP, or a cascade configuration withAPs wirelessly connected to the fiber-connected AP in a multi-hopfashion.

It is desired to densify the network with a large number of accesspoints (AP:s), each one serving a number of CPE:s inside itscorresponding relatively small cell area. Compared to the cases with fewmacro base stations covering a wide area, less path loss/shadowing, andhigher Line Of Sight (LOS) connection probability are expected in densesmall-cell networks. As a result, better channel quality is experiencedin these short-range links, compared to the cases with few macro basestations.

Among the advantageous of IAB networks are the followings:

Cost Reduction:

A fiber optic link is relatively expensive in metropolitan areas, with amajority of the total figure tied to trenching and installation. Forthis reason, as well as the traffic jams and infrastructuredisplacements, some cities have considered a moratorium on fibertrenching specially in historical areas. In such scenarios, millimeterwave-based wireless backhaul is the best alternative providing almostthe same rate as fiber optic with significantly less price and nodigging.

Link Quality Enhancement:

Compared to the direct macro base station (BS)-CPE link, less pathloss/shadowing, and higher line-of-sight (LOS) connection probabilityare expected for the wirelessly backhauled AP-CPE connections withinsmall cells. As a result, better channel quality is experienced in suchsmall cells, compared to the cases with direct macro BS-CPE connection.

Long-Term Network Planning:

IAB systems are of most interest in small cell backhaul and fixedwireless access (FWA) networks with stationary APs/CPEs. This makes itpossible to predict the channel quality and perform accurate networkplanning for multiple packet transmissions.

In an IAB network, aggregated data is accumulated from multiple hopswhich leads to high load of the backhaul links as well as highend-to-end and/or scheduling delay. Particularly, the AP-AP backhaullinks transfer an aggregated data of a large number of CPEs served by,e.g., different APs of the multi-hop network. Due to high load of theAP-AP links, the signals may remain in queue for multiple time slots andbe scheduled with large delays which leads to high end-to-endtransmission delay, as well as high buffer requirement. For this reason,it has been suggested to limit the number of hops to ≤2. To be able tosupport a plurality of CPEs/hops in delay-sensitive applications, it isdesired to design efficient transmission methods which not only reducethe buffer cost but also exploit the unique properties of the IABnetworks to reduce the backhauling load/end-to-end transmission delay.

Generally, there is a desire to have a node in a wireless communicationsystem which communicate with at least one other node, where backhaulingload and end-to-end transmission delay are reduced.

SUMMARY

It is an object of the present disclosure to provide a node in awireless communication system which communicate with at least one othernode, where backhauling load and end-to-end transmission delay arereduced.

This object is obtained by means of a first type node in a wirelesscommunication system, where the first type node is adapted tocommunicate with at least one other first type node in the wirelesscommunication system over a corresponding channel, and to transmit afirst plurality of signals to the other first type node. In the case ofthe other first type node requesting re-transmission of a failed signalin the first plurality of signals, the first type node is furtheradapted to receive a limit of tolerable interference from the otherfirst type node, and to re-send the failed signal in a second pluralityof signals to the other first type node, while sharing the spectrum forthe failed signal with an additional signal without exceeding the limitof tolerable interference.

In this manner, the backhauling load and the buffering cost are reducedsignificantly with no error penalty for the CPE:s. Also, the schedulingdelay of the CPE:s is reduced which leads to higher end-to-endthroughput. This may give the chance to increase the number of hopsand/or CPE:s per hop in multi-hop networks, for example multi-hop IABnetworks.

According to some aspects, there is an available spectral resourceaccomplished by means of the sharing of the spectrum, where the firsttype node is adapted to, in the available spectral resource, add asignal that has been delayed queuing.

In this manner, a waiting signal can be included in a followingre-sending using available spectral resources.

According to some aspects, there is an available spectral resourceaccomplished by means of the sharing of the spectrum, where the firsttype node is adapted to, in the available spectral resource, adapt atransmission rate accordingly for at least one signal.

This improves the reliability of CPE:s, in particular high-rate CPE:s.

According to some aspects, the first type node is adapted to re-encodethe decoded signals and to transmit these re-encoded signal to the otherfirst type node with data rates that are adapted to the free spectrumdetermined to be presently available.

In this manner, the free spectrum is used in an efficient manner.

According to some aspects, the first type node is adapted for accesscommunication with a corresponding group of second type nodes via acorresponding access channel, each group of second type nodes comprisingat least one second type node. The communication between the first typenodes is a backhaul communication via at least one correspondingbackhaul channel, and where the backhaul communication and the accesscommunication both are performed by means of a common equipment at thefirst type nodes.

This means that the present disclosure is applicable for JAB networks.

This means that the present disclosure is applicable for JAB networks.

According to some aspects, the first type node is adapted for at leastone diversity method including frequency hopping to be applied to hybridautomatic repeat request (HARQ) protocols.

According to some aspects, the first type node is adapted to communicatewith said other first type node having Chase combining HARQ usingmaximum ratio combining (MRC) at its receiver.

In this manner, the use of the spectral resource is enhanced.

According to some aspects, the first type node is adapted to transmitthe first plurality of signals to the other first type node in atransmission based on orthogonal multiple access (OMA).

According to some aspects, the first type node is adapted to re-send thefailed signal to the other first type node in a transmission based onnon-orthogonal multiple access (NOMA).

In this way, free spectrum can be better used and more resourcesallocated to the CPE:s with high data rates or schedule new CPE(:s)being in the queue. Thus, the buffer requirement is reduced.

This object is also obtained by means of methods and a communicationsystem that are associated with the above advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described more in detail withreference to the appended drawings, where:

FIG. 1 schematically shows a view of a wireless communication system ata first instant corresponding to a first round;

FIG. 2 schematically shows a first example of a view of a wirelesscommunication system at a second instant corresponding to a secondround, following the first instant;

FIG. 3 schematically shows a graphical representation of accumulated SNRfor two instants corresponding to two rounds;

FIG. 4 schematically shows a second example of a view of a wirelesscommunication system at a second instant corresponding to a secondround, following the first instant;

FIG. 5 schematically shows a first type node; and

FIG. 6 shows a flowchart of methods according to embodiments.

DETAILED DESCRIPTION

Aspects of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings. The differentdevices, systems, computer programs and methods disclosed herein can,however, be realized in many different forms and should not be construedas being limited to the aspects set forth herein. Like numbers in thedrawings refer to like elements throughout.

The terminology used herein is for describing aspects of the disclosureonly and is not intended to limit the invention. As used herein, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise.

Network densification takes advantage of wireless backhaul; due to arelatively high installation cost of fiber links, as well as trafficjams and infrastructure displacements, the relatively small applicationpoints (APs) need to be supported by high-rate LOS wireless backhaullinks which motivates so-called integrated access and backhaul (IAB)networks.

With reference to FIG. 1, there is a wireless communication system 1comprising an IAB network with two hops. There are first type nodes AP₀,AP₁, AP₂ in the wireless communication system 1, here in the form of afirst access point AP₀, a second access point AP₁ and a third accesspoint AP₂. The access points AP₀, AP₁, AP₂ are arranged forcommunication with each other in the wireless communication system 1over a corresponding backhaul channel, h_(A01), h_(A12) having a certainchannel quality, generally by means of one of at least one type ofsignal relaying that according to some aspects employs decoding andencoding. According to some aspects, the signal relaying is constitutedby decoding-encoding forward, DF, relaying of a signal.

Each access point AP₀, AP₁, AP₂ is adapted for access communication witha corresponding group of second type nodes U₀₁, U_(0N); U₁₁, U_(1i),U_(1N); U₂₁, U_(2i), U_(2N−1), U_(2N) via a corresponding access channelh₀₁, h_(0N); h₁₁, h_(1i), h_(1N); h₂₁, h_(2i), h_(2N−1), h_(2N),providing wireless access. The second type nodes U₀₁, U_(0N); U₁₁,U_(1i), U_(1N); U₂₁, U_(2i), U_(2N) are here in the form ofcustomer-premises equipments (CPE:s), and generally each group of CPE:sU₀₁, U_(0N); U₁₁, U_(1i), U_(1N); U₂₁, U_(2i), U_(2N) comprises at leastone CPE. In FIG. 1, there is a generalized nomenclature where an integerN of CPE:s, channels and signals is depicted, where the number N can bedifferent for different access points AP₀, AP₁, AP₂ and differentchannels. For example, for the third access point AP₂ there are CPE:sU₂₁, U_(2i), U_(2N), where i is any number between 1 and N. In thismanner, a general nomenclature is used, although in the example thereare three CPE:s. Generally, the number N is at least one.

The communication between the access points AP₀, AP₁, AP₂ is a backhaulcommunication via a corresponding backhaul channel h_(A01), h_(A12), andin the IAB network, the backhaul communication and the accesscommunication are both performed by means of a common equipment at theaccess points AP₀, AP₁, AP₂. The second access point AP₁ and the thirdaccess point AP₂ are wirelessly backhauled by the first access point AP₀connecting to a core network 2 using a fiber connection 5.

In IAB networks, uplink (UL) and downlink (DL) transmission do notfollow the common definition, as both endpoints of the backhaul linksare access points. However, for simplicity, we refer to datatransmission towards (resp. from) the first access point AP₀ as UL(resp. DL) transmission.

Considering FIG. 1 the discussions relate to UL transmission from theCPEs U₂i, ∀i, served by the third access point AP₂, to the first accesspoint AP₀. However, the same discussions can be applied for DLtransmission as well. Also, we present the setup for time-divisionmultiple access (TDMA) setup. However, the same scheme can also beadapted for other resource allocation approaches such as for examplefrequency-division multiple access (FDMA) and code-division multipleaccess (CDMA).

As the number of hops/CPEs per hop increases, the APs need to transferan aggregated data of multiple CPEs accumulated from the previous hops.As a result, the AP-AP backhaul links are heavily loaded, which may leadto high decoding complexity/delay and buffering cost for the APs as wellas large end-to-end transmission delay/low end-to-end throughput for theCPEs. Generally, the CPEs associated with AP_(j) are denoted by U_(jn),n=1, . . . , N where N is the number of CPE:s allocated for each AP.Also, the signal of U_(jn) is represented by x_(jn), ∀i, n. Thefollowing example will be directed towards UL transmission in theAP₂-AP₁-AP₀ route with special attention to the link AP₁-AP₀ between thesecond access point AP₁ and the first access point AP₀ transferring theaccumulated data of CPE:s U_(jn), j=1, 2, n=1, . . . , N to the firstaccess point AP₀. According to some aspects, in this example so-calledChase combining (Type II) HARQ (hybrid automatic repeat request) can beused where the same signal is sent in successive retransmission roundsand the receiver performs maximum ratio combining (MRC) to decode thesignal based on the accumulated copies of the signal. However, thepresent disclosure is applicable for any suitable HARQ protocol. Also, asetup for the least complicated case with two hops and tworetransmissions will be discussed in order to convey an understanding ofthe present disclosure although the present disclosure can be extendedto an arbitrary number of hops/retransmissions. According to someaspects, in the present context, a signal corresponds to a data signalor a data message.

In the following, a first example will be described with reference toFIG. 1 and FIG. 2.

As illustrated in FIG. 1, showing a first instant corresponding to afirst round, the second access point AP₁ is adapted to communicate thefirst access point AP₀ over a first backhaul channel h_(A01), and totransmit a first plurality of signals x₁₁, x_(1i), x_(1N), x₂₁, x_(2i),x_(2N−1) to the first access point AP₀. In this example, there is afailed signal xi in the first plurality of signals x₁₁, x_(1i), x_(1N),x₂₁, x_(2i), x_(2N−1), and the first access point AP₀ then requestsre-transmission of the failed signal x₁₁.

The second access point AP₁ is then adapted to receive a limit oftolerable interference from the first access point AP₀. As illustratedin FIG. 2, showing a second instant corresponding to a second round andfollowing the first instant, the second access point AP₁ is furtheradapted to re-send the failed signal xi in a second plurality of signalsx₁₁, x′_(2i), x′₁₁, x′_(1i), x′_(1N), x′₂₁, x′_(2N−1), x′_(2N), x_(2N)to the first access point AP₀.

In this context it is mentioned that, for the sake of completeness inFIG. 1, the CPE:s U₁₁, U_(1i), U_(1N) served by the second access pointAP₁ are transmitting signals x′₁₁, x′_(1i), x′_(1N), that are going tobe comprised in the second plurality of signals, to the second accesspoint AP₁.

Furthermore, the CPE:s U₂₁, U_(2i), U_(2N) served by the third accesspoint AP₂ are transmitting signals x″₂₁, x″_(2i), x″_(2N−1), x″_(2N),that are going to be in at least one future round and are shown for thesake of completeness.

In FIG. 2, the CPE:s U₁₁, U_(1i), U_(1N) served by the second accesspoint AP₁ are transmitting signals x″₁₁, x″_(1i), x″_(1N) to the secondaccess point AP₁. Furthermore, the CPE:s U₂₁, U_(2i), U_(2N) served bythe third access point AP₂ are transmitting signals x″′₂₁, x″′_(2i),x″′_(2N−1), x″′_(2N). These signals are going to be in at least onefuture round and are shown for the sake of completeness.

According to the present disclosure, when this occurs, the spectrum forthe failed signal xi is shared with an additional signal x′_(2i) withoutexceeding the limit of tolerable interference. This will be describedmore in detail below.

In a wireless communication system 1 as described, for example an IABnetwork with small cell backhaul and fixed wireless access (FWA)networks, with stationary AP:s/CPE:s, the AP-AP links are staticchannels where the channel quality remains constant for a long time.Therefore, the transmission parameters, e.g., rate and power, can be setwith high accuracy such that the data is successfully transmitted withthe maximum achievable rate of the link and a low probability ofrequiring retransmissions. In this way, with proper parameteradaptation, if a signal is not correctly decoded by an AP, for instanceif there is short-term blockage or changes in the fading, the receivedsignal-to-noise ratio (SNR) is only slightly less than the SNR requiredfor successful signal decoding.

With reference to FIG. 3, denoting the received SNR in the first roundby γ and the SNR required for successful signal decoding by {tilde over(γ)}, γ≲{tilde over (γ)} if an AP fails to decode the signal correctly,in other words the received SNR in the first round γ is slightly lessthan the SNR required for successful signal decoding {tilde over (γ)},which results in the failed signal x₁₁. The SNR required for successfulsignal decoding {tilde over (γ)} can be assumed to be fixed, since thebackhaul channel also can be assumed to be fixed. According to someaspects, with for example Chase combining HARQ-based retransmission andMRC at the receiver, the accumulated SNR at the end of the second roundis given by 2γ (in general, nγ after n retransmissions) which, dependingon the channel conditions, may be considerably larger than the SNRrequired for successful signal decoding, i.e., γ≲{tilde over (γ)}<<2γ.That is, by HARQ-based retransmission, the AP-AP link is over-protected,and the AP is provided with the SNR much more than required forsuccessful signal decoding. Thus, it can tolerate some interference aslong as the additive interference power does not deteriorate thesuccessful signal decoding probability of the CPE using retransmissions.

This means that in accordance with the present disclosure, in the secondround, as well as in other possible retransmission rounds, an extra SNRgap 6 is obtained from the accumulated SNR at the end of the secondround 2γ with the deduction of the SNR required for successful signaldecoding {tilde over (γ)} and a safety margin SNR 7. The extra SNR gap 6is used by another CPE such that, while the spectrum is shared bydifferent CPE:s, their successful signal decoding is guaranteed.

According to some aspects, a successive interference cancellation (SIC)scheme is used such that the signal of the paired CPE(:s) are decodedinterference-free. Then, the available spectrum which has become free,according to some aspects due to non-orthogonal multiple access(NOMA)-based transmission, is utilized to improve the data transmissioncondition of other CPE:s or to schedule the CPE:s being in the queue.

With static channels, the transmission parameters, e.g., rate and power,are set with high accuracy such that the signals, the data, istransferred with the maximum achievable rate and a low probability ofrequiring retransmissions. Thus, if the receiving first access point AP₀fails to decode a signal, the received SNR is only slightly less thanthe SNR required for successful signal decoding. On the other hand, withHARQ-based retransmissions the SNR accumulated after multipleretransmissions exceeds much more than the minimum SNR required forsuccessful signal decoding. Thus, the receiver can tolerate someinterference and allow another signal to be transferred in the samespectrum resource, as long as the added interference power is less thanmaximum tolerable SNR loss.

With the channels being assumed to be static, the transmissionparameters, e.g., rate and power, are set with high accuracy such thatthe data is transferred with the maximum achievable rate and a lowprobability of requiring retransmissions. Thus, if the receiving firstaccess point AP₀, fails to decode a signal x₁₁, the received SNR γ isonly slightly less than the SNR {tilde over (γ)} required for successfulsignal decoding. On the other hand, with HARQ-based retransmissions, theSNR 2γ accumulated after multiple retransmissions exceeds much more thanthe minimum SNR required for successful signal decoding. Thus, thereceiving first access point AP₀ can tolerate some interference andallow another signal to be transferred in the same spectrum resource, aslong as the added interference power is less than maximum tolerable SNRloss. Although the above applies to MRC-based HARQ, the same concept isvalid for other HARQ methods Depending on the CPEs' message decodingstatus, an AP, in this example the second access point AP₁, can usedifferent multiple access schemes for data transmission. In the firstround shown in FIG. 1, the messages are transferred in orthogonalresources. If an AP, in this example the first access point AP₀, failsto decode the signal of an CPE, in this example the failed signal x₁₁,it sends a negative acknowledgement (NACK) signal as well as thepossible limit of the tolerable interference to the second access pointAP₁. Then, based on this information, in the second round, the firstaccess point AP₁ may share the spectrum of the failed signal U₁₁ withanother CPE, in this example a shared signal x′_(2i) from acorresponding CPE U_(2i).

Particularly, the retransmission of the failed signal xi is superimposedwith the shared signal x′_(2i) and sent to the first access point AP₀,according to some aspects in NOMA-based fashion. Also, the parametersare set such that successful decoding of these signals x₁₁, x′_(2i) isguaranteed. According to some aspects, at the first access point AP₀, asuccessive interference cancellation (SIC)-based receiver is utilized tofirst decode the failed signal xi based on the two interference-free andinterference-affected copies of its signal. Then, removing the decodedmessage the failed signal x₁₁, the first access point AP₀ decodes theshared signal x′_(2i) interference-free.

In this way, instead of over-protecting the AP-AP link, the availablespectrum is effectively used to reduce the load of the backhaul link.Finally, a spectral resource has become free due to sending the sharedsignal x′_(2i) in the spectrum resource of a first CPE U₁₁ that isassociated with the failed signal x₁₁, and according to some aspects,this spectral resource can be used for handling signals in differentways; two examples are given below.

According to some aspects, in FIG. 1 there is a delayed signal x_(2N),associated with a delayed CPE U_(2N) and belonging to the first round,which has been held in a queue between the second access point AP₁ andthe third access point AP₂. As shown in FIG. 2, the available spectralresource is used for adding the delayed signal x_(2N) in the secondround, together with a corresponding signal x′_(2N) belonging to thesecond round, having been transferred from the third access point AP₂together with the delayed signal x_(2N). This can reduce the schedulingdelay of the CPE:s in the queue. here the delayed CPE U_(2N).

According to some aspects, the available spectral resource is used toadapt a transmission rate accordingly for at least one signal.

In a second example, with reference to FIG. 1 and FIG. 4, there is adelayed signal x_(2N) belonging to the first round that has been held ina queue, and the delayed signal x_(2N) is added in the second round asshown in FIG. 4 at the expense of a following corresponding signalx′_(2N) belonging to the second round but being held in a queue. Here,the available spectral resource is used to adapt the transmission rateaccordingly for a further signal x′_(2N−1) associated with another CPEU_(2N−1) that is a high-rate CPE. This improves the reliability ofCPE:s, in particular high-rate CPE:s.

More in detail, in FIG. 1, showing a first instant corresponding to afirst round, the second access point AP₁ is adapted to communicate thefirst access point AP₀ over a first backhaul channel h_(A01), and totransmit a first plurality of signals x₁₁, x_(1i), x_(1N), x₂₁, x_(2i),x_(2N−1) to the first access point AP₀. In the same way as in the firstexample, there is a failed signal xi in the first plurality of signalsx₁₁, x_(1i), x_(1N), x₂₁, x_(2i), x_(2N−1), and the first access pointAP₀ then requests re-transmission of the failed signal x₁₁.

The second access point AP₁ is then adapted to receive a limit oftolerable interference from the first access point AP₀. As illustratedin FIG. 4, showing a second instant corresponding to a second round andfollowing the first instant, the second access point AP₁ is furtheradapted to re-send the failed signal x₁₁ in a second plurality ofsignals x₁₁, x′_(2i), x′_(1i), x′_(1N), x′₂₁, x′_(2N−1), x_(2N) to thefirst access point AP₀ while sharing the spectrum for the failed signalx₁₁ with an additional signal x′_(2i) without exceeding the limit oftolerable interference. As mentioned above, a signal x′_(2N) belongingto the second round is held in a queue, while the available spectralresource is used to adapt the transmission rate accordingly for afurther signal x′_(2N−1) associated with another CPE U_(2N−1) that hereis a high-rate CPE.

In FIG. 4, the CPE:s U₁₁, U_(1i), U_(1N) served by the second accesspoint AP₁ are transmitting signals x″₁₁, x″_(1i), x″_(1N) to the secondaccess point AP₁. Furthermore, the CPE:s U₂₁, U_(2i), U_(2N) served bythe third access point AP₂ are transmitting signals x″′₂₁, x″′_(2i),x″′_(2N−1), x″′_(2N). These signals are going to be in at least onefuture round and are shown for the sake of completeness.

In the following, the present disclosure will be described more indetail in a number of steps.

Step 1: In a first round, a first plurality of signals x₁₁, x_(1i),x_(1N), x₂₁, x_(2i), x_(2N−1) are transferred from the second accesspoint AP₁ to the first access point AP₀ in an orthogonal multiple access(OMA)-based scheme. Also, the first access point AP₀ uses a typicalOMA-based receiver to decode the messages.

Step 2: If the first access point AP₀ fails to correctly decode a signalof a CPE, a failed signal x₁₁, it compares the received SNR γ with theSNR {tilde over (γ)} required for successful signal decoding and findsout the maximum interference power that it can tolerate in a followingretransmission round. Then, the first access point AP₀ sends a negativeacknowledgement (NACK) signal along with a signal indicating the maximumtolerable interference power 6 to the second access point AP₁ preferablythere is safe SNR zone 7 to guarantee that the failed signal x₁₁ can becorrectly decoded in the retransmissions.

Step 3: Receiving these information, the second access point AP₁ firstuses the CPE:s' data rates to find the CPE:s whose successful messagedecoding probability can be guaranteed, according to some aspects withNOMA-based transmission, and the available interfering power. In thefollowing, a channel gain of the AP₁-AP₀ link between the second accesspoint AP₁ and the first access point AP₀ is represented by g and theadditive noise power of the first access point AP₀ is normalized to 1.The transmission power considered by the second access point AP₁ fortransmission of x_(ij) is represented by P_(ij) where P_(ij)≤P, with Pbeing the maximum output power of the second access point AP₁. Then, inthe first round 1, the received SNR γ=Pg and with two CPE:s sharing thesame spectrum in the second round, the accumulated SNR for the failedsignal x₁₁ is given by

$\begin{matrix}{{{\overset{\_}{\gamma}}_{11} = {{Pg} + \frac{P_{11}g}{1 + {\hat{P}\; g}}}},} & (1)\end{matrix}$

with P₁₁+{circumflex over (P)}=P where P₁₁ is the power allocated to themessage the failed signal x₁₁ in the second round, and {circumflex over(P)} is the power of the interfering signal. Then, to guaranteesuccessful message decoding of U₁₁,

$\begin{matrix}{{{Pg} + \frac{P_{11}g}{1 + {\hat{P}\; g}}} \geq {\overset{\sim}{\gamma} + \theta}} & (2)\end{matrix}$

where θ≥0 is a threshold denoted by the safe zone 7 in FIG. 3,considered by the network designer for guaranteeing the successfulmessage decoding of the failed signal x₁₁. Using equation (2) andP₁₁+{circumflex over (P)}=P, the transmission power for theretransmission of the failed signal x₁₁ is given by

$\begin{matrix}{{P_{1} = \frac{c\left( {1 + {gP}} \right)}{g\left( {1 + c} \right)}},{c = {\overset{\sim}{\gamma} + \theta - {Pg}}},} & (3)\end{matrix}$

and the power available for data transmission of the other sharing CPEis obtained as

$\begin{matrix}{\hat{P} = {\frac{{gP} - c}{g\left( {1 + c} \right)}.}} & (4)\end{matrix}$

Then, the second access point AP₁ finds the CPE with the maximum datarate that can be supported by the available transmission power. That is,the second access point AP₁ finds the CPE:s such that

log(1+{circumflex over (P)}g)≥r _(ji)  (5)

where r_(ji) is the data rate of U_(ji) and {circumflex over (P)} is theavailable power found in equation (4). Here, equation (5) is based onthe fact that the message of the interfering CPE is decoded at the firstaccess point AP₀ by a SIC-based receiver. Then the second access pointAP₁ selects the CPE with the highest data rate such that equation (5) issatisfied. In this example, it is assumed that this CPE is a selectedCPE U_(2i) that in this example is a second CPE U_(2i).

Step 4: The second access point AP₁ allocates powers P₁₁ and {circumflexover (P)} to the retransmission of the failed signal x₁₁ and the sharedsignal x_(2i) of the second CPE U_(2i), respectively, superimposes theirsignals and sends a combined signal x₁₁+x_(2i) to the first access pointAP₀ in the spectrum resource which was initially allocated to the failedsignal x₁₁ in the first round. Then, the spectrum resource which waspreviously allocated to the shared signal x_(2i) in the first round isnow free and is used by the second access point AP₁ to adapt thetransmission parameter of another, possibly high-rate, CPE, denoted byx_(2N−1) in FIG. 4, or schedule a new CPE, denoted by x_(2N) in FIG. 2,which has been in queue.

Step 5: At the first access point AP₀, the decoding scheme is adapted,and a SIC-based receiver is used to decode the signals of the CPE:s U₁₁,U_(2i). First, an MRC-based receiver is used to combine the twointerference-free (received in the first round) andinterference-affected (received in the second round) copies of thefailed signal x₁₁. Due to power allocation based on equation (3)-(4),the first access point AP₀ can correctly decode the failed signal x₁₁ inthe second round with very high probability. Then, removing the decodedfailed signal x₁₁ from the received signal, the first access point AP₀decodes the shared signal x_(2i) of the second CPE U_(2i)interference-free which, because of power and rate allocation based onequations (4)-(5), can be correctly decoded with high probability.

Step 6: Based on updated resource allocation of the CPE:s, allAP:s/CPE:s synchronize their signals and determine their timing.

In this way, the present disclosure reduces the load of the backhaullink, improves the transmission reliability for the high-rate CPE:s andreduces the scheduling delay/buffering cost because:

-   -   the spectrum is not wasted for over-protecting the AP-AP links        and, instead, is reused to transfer multiple signals on the same        spectrum with no error penalty for the CPE:s sharing the same        spectrum, and    -   NOMA-based transmission gives the chance to use the free        spectrum and allocate more resources to the CPE:s with high data        rates or schedule new CPE(:s) being in the queue. Thus, the        buffer requirement is reduced by the proposed method.

As shown in FIG. 5, according to some aspects, the second access pointAP₁ comprises a processor unit 3 that is adapted to instruct the secondaccess point AP₁ to:

-   -   communicate with the first access point AP₀ in the wireless        communication system 1 over a corresponding channel h_(A01), and        to    -   transmit a first plurality of signals x₁₁, x_(1i), x_(1N), x₂₁,        x_(2i), x_(2N−1) to the first access point AP₀.

In the case of the first access point AP₀ requesting re-transmission ofa failed signal xi in the first plurality of signals x₁₁, x_(1i),x_(1N), x₂₁, x_(2i), x_(2N−1), the processor unit 3 that is furtheradapted to instruct the second access point AP₁ to:

-   -   receive a limit of tolerable interference from the first access        point AP₀, and to    -   re-send the failed signal xi in a second plurality of signals        x₁₁, x′_(2i), x′_(1i), x′_(1N), x′₂₁, x′_(2N−1), x′_(2N),        x_(2N); x₁₁, x′_(2i), x′_(1i), x′_(1N), x′₂₁, x′_(2N−1), x_(2N)        to the first access point AP₀ while sharing the spectrum for the        failed signal x₁₁ with an additional signal x′_(2i) without        exceeding the limit of tolerable interference.

With reference to FIG. 6, the present disclosure also relates to amethod in a first type node AP₁ in a wireless communication system 1.The method comprises communicating S1 with at least one other first typenode AP₀ in the wireless communication system 1 over a correspondingchannel h_(A01); and transmitting S2 a first plurality of signals x₁₁,x_(1i), x_(1N), x₂₁, x_(2i), x_(2N−1) to the other first type node AP₀.

In the case C1 of the other first type node AP₀ requestingre-transmission of a failed signal x₁₁ in the first plurality of signalsx₁₁, x_(1i), x_(1N), x₂₁, x_(2i), x_(2N−1), the method further comprisesreceiving S3 a limit of tolerable interference from the other first typenode AP₀ in case of the other first type node AP₀ requestingre-transmission of a failed signal x₁₁ in the first plurality of signalsx₁₁, x_(1i), x_(1N), x₂₁, x_(2i), x_(2N−1); and re-sending S4 the failedsignal x₁₁ in a second plurality of signals x₁₁, x′_(2i), x′_(1i),x′_(1N), x′₂₁, x′_(2N−1), x′_(2N), x_(2N); x₁₁, x′_(2i), x′_(1i),x′_(1N), x′₂₁, x′_(2N−1), x_(2N) to the other first type node AP₀ whilesharing the spectrum for the failed signal x₁₁ with an additional signalx′_(2i) without exceeding the limit of tolerable interference.

According to some aspects, there is an available spectral resourceaccomplished by means of the sharing of the spectrum, where the methodcomprises, in the available spectral resource, adding S5 a signal x_(N)that has been delayed queuing.

According to some aspects, there is an available spectral resourceaccomplished by means of the sharing of the spectrum, where the methodcomprises, in the available spectral resource, adapting S6 atransmission rate accordingly for at least one signal x′_(2N−1).

According to some aspects, the method comprises re-encoding the decodedsignals and transmitting these re-encoded signal to the other first typenode AP₀ with data rates that are adapted to the free spectrumdetermined to be presently available.

According to some aspects, the first type node AP₁ is used for accesscommunication with a corresponding group of second type nodes U₀₁,U_(0N); U₁₁, U_(1i), U_(1N); U₂₁, U_(2i), U_(2N) via a correspondingaccess channel h₀₁, h_(0N); h₁₁, h_(1i), h_(1N); h₂₁, h_(2i), h_(2N),each group of second type nodes U₀₁, U_(0N); U₁₁, U_(1i), U_(1N); U₂₁,U_(2i), U_(2N) comprising at least one second type node U₀₁, U_(0N);U₁₁, U_(1i), U_(1N); U₂₁, U_(2i), U_(2N), where the communicationbetween the first type nodes AP₀, AP₁, AP₂ is a backhaul communicationvia at least one corresponding backhaul channel h_(A01), h_(A12), andwhere the backhaul communication and the access communication both areperformed by means of a common equipment at the first type nodes AP₀,AP₁, AP₂.

According to some aspects, the first type node AP₁ is used for at leastone diversity method including frequency hopping to be applied to hybridautomatic repeat request, HARQ, protocols.

According to some aspects, the method comprises communicating with saidother first type node AP₀ having Chase combining HARQ using maximumratio combining, MRC, at its receiver.

According to some aspects, the method comprises transmitting the firstplurality of signals x₁₁, x_(1i), x_(1N), x₂₁, x_(2i), x_(2N−1) to theother first type node AP₀ in a transmission based on orthogonal multipleaccess, OMA.

According to some aspects, the method comprises re-sending the failedsignal xi to the other first type node AP₀ in a transmission based onnon-orthogonal multiple access, NOMA.

The present disclosure is not limited to the above, but may vary freelywithin the scope of the appended claims. For example, the presentdisclosure has been described for the least complicated cases with twohops, two CPE:s sharing the same spectrum and two retransmissionsrounds. However, the same discussions can be applied to the cases witharbitrary number of hops, sharing CPE:s and retransmission rounds.Particularly, the efficiency of the proposed scheme increases with thenumber of retransmissions. This is because the tolerable interferencepower increases with the number of retransmission rounds which makes itpossible to pair multiple CPE:s.

In the examples described with reference to FIG. 3 and FIG. 4, none ofthe spectrum-sharing CPE:s lose their performance. This is because:

1) the power terms are allocated such that successful message decodingof the first CPE U₁₁ is guaranteed and,

2) with SIC-based receiver, the signal of the second CPE U_(2i) isdecoded interference-free.

The present disclosure is applicable for both frequency division duplex(FDD) and time division duplex (TDD) schemes, different HARQ protocolsas well as for both uplink (UL) and downlink (DL) transmission.

According to some aspects, the present disclosure can easily extended tothe cases with arbitrary number of hops, different relaying approachesor star-like network configuration.

The efficiency depends a lot on the availability of the channel stateinformation (CSI) and the predictability of the channel condition suchthat the transmission parameters can be properly set with no errorpenalty for the paired CPE:s. This information can be provided in IABnetworks due to the stationary network configuration and the staticchannels conditions.

Sometimes, to increase the successful message decoding probability,different diversity methods such as frequency hopping are applied toHARQ protocols. The present disclosure is well applicable to thesetechniques as long as the channels quality are known by the AP:s.

The present disclosure has according to an example been described withChase combining HARQ using MRC at the receiver. However, the presentdisclosure is applicable for many different types of receiverconfigurations, e.g., incremental redundancy (Type III), HARQ protocols.Finally, the same discussions can be extended for the cases withdifferent multiplexing schemes as well as for DL transmission.

The present disclosure relates to an efficient data transmissiontechnique that according to some aspects is suitable for multi-hop IABnetworks using hybrid automatic repeat request (HARQ). The objective isto reduce the backhauling load of the AP-AP links transferring anaggregated data of multiple CPE:s as well as to reduce the bufferingcost. Depending on the CPE:s' data rates, the AP:s may use the samespectrum to transfer the messages of different CPE:s in the HARQ-basedretransmission rounds. According to some aspects, if an AP fails todecode the message of a CPE, in the next retransmission round(s) itsallocated spectrum may be shared by another CPE in non-orthogonalmultiple access (NOMA)-based fashion and the message decoding approachis adapted correspondingly. In this way, the spectrum is not wasted forover-protecting the AP-AP links and, instead, is used to reduce the loadof the backhaul links with no penalty for the sharing CPEs. Also, theNOMA-based data transmission gives the chance to allocate the freespectrum to other CPEs, reducing the scheduling delay/bufferrequirement.

Above, a case has been described where a SIC-based receiver has beenused to first decode one of the signals and then decode the secondsignal interference-free. According to some aspects, another option isthat SIC is not used; instead, a normal receiver is used and the signalsare decoded in the presence of interferences. This alternative supportsless data rates, but the receiver is less complex. Other alternativesare of course conceivable, only a few examples having been providedhere.

Using a NOMA-based transmission in the retransmission rounds along withthe proposed resource reallocation scheme and decoder adaptation methodreduces the backhauling load and the buffering cost significantly withno error penalty for the CPE:s. Also, the scheduling delay of the CPE:sis reduced which leads to higher end-to-end throughput. This may givethe chance to increase the number of hops and/or CPE:s per hop inmulti-hop IAB networks.

In FIG. 1, FIG. 2 and FIG. 4 it is illustrated that the CPE:s U₀₁,U_(0N) served by the first access point AP₀ are transmitting signalsx₀₁, x_(0N), x′₀₁, x′_(0N), in the rounds described only to illustratethat the first access point AP₀ at the same time also can serve aplurality of CPE:s U₀₁, U_(0N).

The present disclosure can be applied for any type of transmissionbetween any first type nodes AP₀, AP₁, AP₂ in the wireless communicationsystem 1. Using Chase combining HARQ-based retransmission and MRC isonly an example.

Generally, the present disclosure relates to a first type node AP₁ in awireless communication system 1, wherein the first type node AP₁ isadapted to:

-   -   communicate with at least one other first type node AP₀ in the        wireless communication system 1 over a corresponding channel        h_(A01), and    -   transmit a first plurality of signals x₁₁, x_(1i), x_(1N), x₂₁,        x_(2i), x_(2N−1) to the other first type node AP₀.

In the case of the other first type node AP₀ requesting re-transmissionof a failed signal xi in the first plurality of signals x₁₁, x_(1i),x_(1N), x₂₁, x_(2i), x_(2N−1), the first type node AP₁ is furtheradapted to:

-   -   receive a limit of tolerable interference from the other first        type node AP₀, and    -   re-send the failed signal x₁₁ in a second plurality of signals        x₁₁, x′_(2i), x′_(1i), x′_(1N), x′₂₁, x′_(2N−1), x′_(2N),        x_(2N); x₁₁, x′_(2i), x′_(1i), x′_(1N), x′₂₁, x′_(2N−1), x_(2N)        to the other first type node AP₀ while sharing the spectrum for        the failed signal xi with an additional signal x′_(2i) without        exceeding the limit of tolerable interference.

According to some aspects, there is an available spectral resourceaccomplished by means of the sharing of the spectrum, where the firsttype node AP₁ is adapted to, in the available spectral resource, add asignal x_(N) that has been delayed queuing.

According to some aspects, there is an available spectral resourceaccomplished by means of the sharing of the spectrum, where the firsttype node AP₁ is adapted to, in the available spectral resource, adapt atransmission rate accordingly for at least one signal x′_(2N−1).

According to some aspects, the first type node AP₁ is adapted tore-encode the decoded signals and to transmit these re-encoded signal tothe other first type node AP₀ with data rates that are adapted to thefree spectrum determined to be presently available.

According to some aspects, the first type node AP₁ is adapted for accesscommunication with a corresponding group of second type nodes U₀₁,U_(0N); U₁₁, U_(1i), U_(1N); U₂₁, U_(2i), U_(2N) via a correspondingaccess channel h₀₁, h_(0N); h₁₁, h_(1i), h_(1N); h₂₁, h_(2i), h_(2N),each group of second type nodes U₀₁, U_(0N); U₁₁, U_(1i), U_(1N); U₂₁,U_(2i), U_(2N) comprising at least one second type node U₀₁, U_(0N);U₁₁, U_(1i), U_(1N); U₂₁, U_(2i), U_(2N), where the communicationbetween the first type nodes AP₀, AP₁, AP₂ is a backhaul communicationvia at least one corresponding backhaul channel h_(A01), h_(A12), andwhere the backhaul communication and the access communication both areperformed by means of a common equipment at the first type nodes AP₀,AP₁, AP₂.

According to some aspects, the first type node AP₁ is adapted for atleast one diversity method including frequency hopping to be applied tohybrid automatic repeat request, HARQ, protocols.

According to some aspects, the first type node AP₁ is adapted tocommunicate with said other first type node AP₀ having Chase combiningHARQ using maximum ratio combining, MRC, at its receiver.

According to some aspects, the first type node AP₁ is adapted totransmit the first plurality of signals x₁₁, x_(1i), x_(1N), x₂₁,x_(2i), x_(2N−1) to the other first type node AP₀ in a transmissionbased on orthogonal multiple access, OMA.

According to some aspects, the first type node AP₁ is adapted to re-sendthe failed signal x₁₁ to the other first type node AP₀ in a transmissionbased on non-orthogonal multiple access, NOMA. Generally, the presentdisclosure also relates to a wireless communication system 1 comprisingan integrated access and backhaul, IAB, network which in turn at leastcomprises the first type node AP₁ and the other first type node AP₀according to the above.

1. A first type node in a wireless communication system, wherein thefirst type node is adapted to: communicate with at least one other firsttype node in the wireless communication system over a correspondingchannel, and transmit a first plurality of signals to the other firsttype node, where, in the case of the other first type node requestingre-transmission of a failed signal in the first plurality of signals,the first type node is further adapted to: receive a limit of tolerableinterference from the other first type node, and re-send the failedsignal in a second plurality of signals to the other first type nodewhile sharing the spectrum for the failed signal with an additionalsignal without exceeding the limit of tolerable interference.
 2. Thefirst type node according to claim 1, wherein there is an availablespectral resource accomplished by way of the sharing of the spectrum,where the first type node is adapted to, in the available spectralresource, add a signal that has been delayed queuing.
 3. The first typenode according to claim 1, wherein there is an available spectralresource accomplished by way of the sharing of the spectrum, where thefirst type node is adapted to, in the available spectral resource, adapta transmission rate accordingly for at least one signal.
 4. The firsttype node according to claim 1, wherein the first type node is adaptedto re-encode the decoded signals and to transmit these re-encodedsignals to the other first type node with data rates that are adapted tothe free spectrum determined to be presently available.
 5. The firsttype node according to claim 1, wherein the first type node is adaptedfor access communication with a corresponding group of second type nodesvia a corresponding access channel, each group of second type nodescomprising at least one second type node, where the communicationbetween the first type nodes is a backhaul communication via at leastone corresponding backhaul channel, and where the backhaul communicationand the access communication both are performed by way of a commonequipment at the first type nodes.
 6. The first type node according toclaim 1, wherein the first type node is adapted for at least onediversity method including frequency hopping to be applied to hybridautomatic repeat request, HARQ, protocols.
 7. The first type nodeaccording to claim 6, wherein the first type node is adapted tocommunicate with said other first type node having Chase combining HARQusing maximum ratio combining, MRC, at its receiver.
 8. The first typenode according to claim 1, wherein the first type node is adapted totransmit the first plurality of signals to the other first type node ina transmission based on orthogonal multiple access, OMA.
 9. The firsttype node according to claim 1, wherein the first type node is adaptedto re-send the failed signal to the other first type node in atransmission based on non-orthogonal multiple access, NOMA.
 10. A methodin a first type node in a wireless communication system, the methodcomprising: communicating with at least one other first type node in thewireless communication system over a corresponding channel; andtransmitting a first plurality of signals to the other first type node;where, in the case of the other first type node requestingre-transmission of a failed signal in the first plurality of signals,the method further comprises: receiving a limit of tolerableinterference from the other first type node in case of the other firsttype node requesting re-transmission of a failed signal in the firstplurality of signals; and re-sending the failed signal in a secondplurality of signals to the other first type node while sharing thespectrum for the failed signal with an additional signal withoutexceeding the limit of tolerable interference.
 11. The method accordingto claim 10, wherein there is an available spectral resourceaccomplished by way of the sharing of the spectrum, where the methodcomprises, in the available spectral resource, adding a signal that hasbeen delayed queuing.
 12. The method according to claim 10, whereinthere is an available spectral resource accomplished by way of thesharing of the spectrum, where the method comprises, in the availablespectral resource, adapting a transmission rate accordingly for at leastone signal.
 13. The method according to claim 10, wherein the methodcomprises re-encoding the decoded signals and transmitting thesere-encoded signal to the other first type node with data rates that areadapted to the free spectrum determined to be presently available. 14.The method according to claim 10, wherein the first type node is usedfor access communication with a corresponding group of second type nodesvia a corresponding access channel, each group of second type nodescomprising at least one second type node, where the communicationbetween the first type nodes is a backhaul communication via at leastone corresponding backhaul channel, and where the backhaul communicationand the access communication both are performed by way of a commonequipment at the first type nodes.
 15. The method according to claim 10,wherein the first type node is used for at least one diversity methodincluding frequency hopping to be applied to hybrid automatic repeatrequest, HARQ, protocols.
 16. The method according to claim 15, whereinthe method comprises communicating with said other first type nodehaving Chase combining HARQ using maximum ratio combining, MRC, at itsreceiver.
 17. The method according to claim 10, wherein the methodcomprises transmitting the first plurality of signals to the other firsttype node in a transmission based on orthogonal multiple access, OMA.18. The method according to claim 10, wherein the method comprisesre-sending the failed signal to the other first type node in atransmission based on non-orthogonal multiple access, NOMA.
 19. Awireless communication system comprising an integrated access andbackhaul, IAB, network which in turn comprises at least the first typenode and the other first type node according to claim 1.